This invention relates to a fluidized bed reactor and a method of operating same and, more particularly, to such a reactor and method in which a solids recycle seal system is provided within the furnace section of the reactor.
Fluidized bed reactors, such as combustors, gasifiers, steam generators, and the like, are well known. In these arrangements, air is passed through a bed of particulate material, including a fossil fuel such as coal and a sorbent for the sulfur generated as a result of combustion of the coal, to fluidize the bed and to promote the combustion of the fuel at a relatively low temperature. The entrained particulate solids are separated externally of the bed and recycled back into the bed. The heat produced by the fluidized bed is utilized in various applications such as the generation of steam, which results in an attractive combination of high heat release, high sulfur capture, low nitrogen oxides emissions and fuel flexibility.
The most typical fluidized bed reactor is commonly referred to as a "bubbling" fluidized bed in which the bed of particulate material has a relatively high density and a well defined, or discrete, upper surface.
Other types of fluidized bed reactors utilize a "circulating" fluidized bed. According to these processes, the fluidized bed density is well below that of a typical bubbling fluidized bed, the air velocity is greater than that of a bubbling bed, and the flue gases passing through the bed entrain a substantial amount of particulate solids and are substantially saturated therewith. Circulating fluidized beds are also characterized by relatively high solids recycling which makes it insensitive to fuel heat release patterns, thus minimizing temperature variations, and therefore, stabilizing the emissions at a low level. The high solids recycling improves the efficiency of the mechanical device used to separate the gas from the solids for solids recycle, and the resulting increase in sulfur collection and fuel residence times reduces the sorbent and fuel consumption.
However, several problems do exist in connection with these types of fluidized bed reactors. For example, a sealing device such as a seal pot, a "J" valve, a syphon seal, a loop seal, an "L" valve, or similar device is required between the low pressure separator outlet and the higher pressure furnace section of the reactor to prevent a back flow of gases and solids from the furnace section to the outlet of the separator.